Measuring Neonatal Measuring Neonatal Lung VolumeLung Volume

Advisor: Dr. Bill WalshAdvisor: Dr. Bill Walsh

Doug AndersonDoug Anderson

David LammleinDavid Lammlein

Janine McKinnonJanine McKinnon

BackgroundBackground

The Division of Neonatology at The Division of Neonatology at Vanderbilt Children’s Hospital has Vanderbilt Children’s Hospital has an interest in determining the an interest in determining the Functional Residual Capacity Functional Residual Capacity (FRC) in neonates who are (FRC) in neonates who are mechanically ventilated mechanically ventilated

Neonatal Intensive Care Unit Neonatal Intensive Care Unit (NICU) includes 60 intensive and (NICU) includes 60 intensive and intermediate beds, a 3 bed ECMO intermediate beds, a 3 bed ECMO unit, and 10 bed intensive care unit, and 10 bed intensive care nurserynursery

Methods must be simple, non-Methods must be simple, non-invasive, and allow free access to invasive, and allow free access to neonatesneonates

Functional Residual Capacity Functional Residual Capacity (FRC)(FRC)

Functional Residual Capacity Functional Residual Capacity (FRC) of the human lung is the (FRC) of the human lung is the volume volume remaining in remaining in the the lungs lungs at resting expiratory levelat resting expiratory level Equivalent to the alveolar Equivalent to the alveolar

volume (Va) which volume (Va) which contains 60-70% of the contains 60-70% of the total lung volumetotal lung volume

Normal FRC in adults is Normal FRC in adults is 1.8 to 3.4 L1.8 to 3.4 L

Estimated FRC in healthy Estimated FRC in healthy neonates 5 to 12 mLneonates 5 to 12 mL

Problem DescriptionProblem Description

Problem:Problem: Too small a FRC results in the inability to Too small a FRC results in the inability to oxygenate and consequently death because blood oxygenate and consequently death because blood entering the lung actually exits the lung without coming entering the lung actually exits the lung without coming into contact with a gas surfaceinto contact with a gas surface

Solution:Solution: Designing a device that measures FRC in Designing a device that measures FRC in neonates can allow doctors and researchers to optimize neonates can allow doctors and researchers to optimize ventilator settings so as to prevent this sort of shunting ventilator settings so as to prevent this sort of shunting and also provide them with better methods to assist the and also provide them with better methods to assist the breathing in neonates especially those who are born breathing in neonates especially those who are born premature and suffer from respiratory distress syndrome premature and suffer from respiratory distress syndrome and other lung pathologiesand other lung pathologies

Measuring FRCMeasuring FRC

Helium Dilution Method•Inspiration of known [He]

•Gas in lungs dilutes He and [He] drops

•Gases equilibrate

•Measure difference in [He] to determine initial lung volume

Nitrogen Washout Method•Unknown FRC contains about 78% N2 and an unknown amount of O2 and CO2

•Washout N2 by breathing 100% O2

•Exhale so that expired [N2] falls between 1 and 1.5%

Previous Attempts to Measure Previous Attempts to Measure FRC IFRC I

Critical Care Medicine (1980)Critical Care Medicine (1980) Estimating FRC of newborn infants receiving continuous positive Estimating FRC of newborn infants receiving continuous positive

airway pressure (CPAP)airway pressure (CPAP) Four-breath nitrogen washout techniqueFour-breath nitrogen washout technique

Reduces the period of breathing pure oxygenReduces the period of breathing pure oxygen

Mechanical lung modelMechanical lung model Infants with Respiratory Distress Syndrome (RDS)Infants with Respiratory Distress Syndrome (RDS)

Journal of Applied Physiology (1992)Journal of Applied Physiology (1992) Modification of computerized tracer gas (SF6) washout methodModification of computerized tracer gas (SF6) washout method Designed for serial measurements of FRC and ventilation Designed for serial measurements of FRC and ventilation

homogeneity in mechanically ventilated infantshomogeneity in mechanically ventilated infants Very low birth weightVery low birth weight Tidal volume down to 4 mLTidal volume down to 4 mL Mild to moderate RDSMild to moderate RDS

FRC increased with body weightFRC increased with body weight FRC (mL) = -1.4 + 17 x weight (kg)FRC (mL) = -1.4 + 17 x weight (kg)

Previous Attempts to Measure Previous Attempts to Measure FRC IIFRC II

Pediatric Pulmonology (1997)Pediatric Pulmonology (1997) Compared standard N2 washout technique for Compared standard N2 washout technique for

measuring FRC with a modified technique using heliox measuring FRC with a modified technique using heliox as a washout gasas a washout gas

Volumes can be measured with high precision and Volumes can be measured with high precision and reproducibility, even in premature infants with low lung reproducibility, even in premature infants with low lung volumes and/or high baseline FIO2volumes and/or high baseline FIO2

Correction factor may be needed because using helioxCorrection factor may be needed because using heliox

Previous Attempts to Measure Previous Attempts to Measure FRC IIIFRC III

Our ChoiceOur Choice

1978 - A Method for Measuring Functional 1978 - A Method for Measuring Functional Residual Capacity in Neonates with Residual Capacity in Neonates with Endotracheal TubesEndotracheal Tubes

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The DeviceThe Device

ResultsResults

In VitroIn Vitro Confirmed expected exponential relationshipConfirmed expected exponential relationship Real vs. Calculated: r = 0.995, p<0.001Real vs. Calculated: r = 0.995, p<0.001

In VivoIn Vivo

Used in infants as small as 600 gUsed in infants as small as 600 g

CPAP (cm HCPAP (cm H22O)O)

00 33

FRCFRC 22.0 22.0 1.9 1.9 25.8 25.8 1.4 1.4

NN 1515 3030

AdvantagesAdvantages

Easy to set upEasy to set up Uses common equipmentUses common equipment Can be used for a large range of infantsCan be used for a large range of infants Useable with both CPAP and ventilator Useable with both CPAP and ventilator

supportsupport Relatively inexpensiveRelatively inexpensive

LimitationLimitation

Breathing rate and tidal volume assumed Breathing rate and tidal volume assumed constantconstant No calculation if minute ventilation (respiratory No calculation if minute ventilation (respiratory

rate X tidal volume) changed by more than rate X tidal volume) changed by more than 25% over measurement period25% over measurement period

Obstructive diseases may delay Obstructive diseases may delay equilibrationequilibration

Research into subsequent efforts into this Research into subsequent efforts into this limitation is ongoinglimitation is ongoing

Closed Loop Helium Dilution Closed Loop Helium Dilution System for Measuring FRCSystem for Measuring FRC

Assembling Prototype Assembling Prototype

Compile list of necessary supplies and Compile list of necessary supplies and equipmentequipment

Procure or obtain access to all necessary Procure or obtain access to all necessary itemsitems

Assemble and test prototypeAssemble and test prototype Refine and upgrade prototypeRefine and upgrade prototype

Supplies and EquipmentSupplies and Equipment

Medical grade tubingMedical grade tubing Valves and stopcocksValves and stopcocks Expandable Expandable

membranesmembranes Solenoid ValveSolenoid Valve

Inexpensive Purchaseables

VUMC Equipment

Air PumpsAir Pumps

Digital Helium MeterDigital Helium Meter

Pulmonary Function MachinePulmonary Function Machine

Design GoalsDesign Goals

Use primarily existing equipmentUse primarily existing equipment Avoid complicated, dangerous, or Avoid complicated, dangerous, or

invasive proceduresinvasive procedures Allow for uncooperative nature of Allow for uncooperative nature of

infantsinfants Mobility of deviceMobility of device Continued free access to Continued free access to

neonateneonate

Market PotentialMarket Potential

Clients: Neonatal Intensive Care UnitsClients: Neonatal Intensive Care Units

Competitors: No current patents exist on this Competitors: No current patents exist on this exact device; however, other more costly exact device; however, other more costly methods (i.e. tomography, ultrasonic flow meter) methods (i.e. tomography, ultrasonic flow meter) exist.exist.

Production: Creating simple modification to Production: Creating simple modification to existing equipment will result in lower production existing equipment will result in lower production costs and overhead.costs and overhead.

Social ImpactSocial Impact

Profound: Families and Profound: Families and friends of critically ill friends of critically ill neonatesneonates

Minimal: Environment, Minimal: Environment, helium is an inert gashelium is an inert gas

ReferencesReferences

Schwartz JG, Fox WW, Shaffer TH. A Method Schwartz JG, Fox WW, Shaffer TH. A Method for Measuring Functional Residual Capacity in for Measuring Functional Residual Capacity in Neonates with Endotracheal Tubes. IEEE Neonates with Endotracheal Tubes. IEEE Trans. On Biomed. Engineering. 25(3): 304-7. Trans. On Biomed. Engineering. 25(3): 304-7. 1978 May.1978 May.

Critical Care Medicine. 8(11): 667-70. 1980 Nov.Critical Care Medicine. 8(11): 667-70. 1980 Nov. Journal of Applied Physiology. 73(1): 276-83. Journal of Applied Physiology. 73(1): 276-83.

1992 July.1992 July. Pediatric Pulmonology. 23(6): 434-41. 1997 Pediatric Pulmonology. 23(6): 434-41. 1997

June.June.

QuestionsQuestions